The recent new environments for usage of disc drive memory systems have intensified design and performance needs including miniaturization and reduced power consumption. Besides traditional computing environments, disc drive memory systems are used more recently by devices including digital cameras, digital video recorders, laser printers, photo copiers, jukeboxes, video games and personal music players. Disc drive memory systems store digital information that is recorded on concentric tracks of a magnetic disc medium. Several discs are rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the stator. One type of motor is known as an in-hub or in-spindle motor, which typically has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and the sleeve, while maintaining alignment of the spindle to the shaft. The read/write heads must be accurately aligned with the storage tracks on the disc to ensure the proper reading and writing of information.
Spindle motors have in the past used conventional ball bearings between the sleeve and the shaft. However, the demand for increased storage capacity and smaller disc drives has led to the design of higher recording area density such that the read/write heads are placed increasingly closer to the disc surface. A slight wobble or run-out in disc rotation can cause the disc to strike the read/write head, possibly damaging the disc drive and resulting in loss of data. Conventional ball bearings exhibit shortcomings in regard to these concerns. Imperfections in the raceways and ball bearing spheres result in vibrations. Also, resistance to mechanical shock and vibration is poor in the case of ball bearings, because of low damping. Vibrations and mechanical shock can result in misalignment between data tracks and the read/write transducer. These shortcomings limit the data track density and overall performance of the disc drive system. Because this rotational accuracy cannot be achieved using ball bearings, disc drives currently utilize a spindle motor having fluid dynamic bearings between a shaft and sleeve to support a hub and the disc for rotation. One alternative bearing design is a hydrodynamic bearing.
In a hydrodynamic bearing, a lubricating fluid such as gas or liquid or air provides a bearing surface between a fixed member and a rotating member of the disc drive. Hydrodynamic bearings eliminate mechanical contact vibration problems experienced by ball bearing systems. Further, hydrodynamic bearings can be scaled to smaller sizes whereas ball bearings have smallness limitations. Dynamic pressure-generating grooves are conventionally formed on a surface of the hydrodynamic bearing journal to generate a localized area of high pressure and provide a transport mechanism for fluid to distribute fluid pressure within the bearing and between the rotating surfaces, enabling the spindle to accurately rotate. These grooves typically include an asymmetric shape to overcome any taper effects formed in a journal bearing and to provide for fluid flow.
Demands of the market and advances in technology have lead to the reduction in the physical size of disc drives. Efforts have been made to design smaller profile disc drives without loss of performance. In reducing size, there is a trend to reduce the axial height of the fluid dynamic bearing motor. One axially reduced sized disc drive currently on the market is the one-inch disc drive used with a CF card type II form factor. However, as motors become shorter in axial height, the spacing between bearing components decreases thereby minimizing the angular or rocking stiffness of the bearings. It has become essential in the industry to design disc drives having even smaller dimensions while maintaining motor stiffness and reduced power consumption. What is needed is a hard disc drive having increased journal bearing stiffness and reduced power consumption for current usage environments.